The role of sediments as carriers and potential sources of contaminants is reviewed. A program of sediment studies will normally consist of a series of objectives of increasing complexity, each drawing part of its information from the preceding data base. The study of dated sediment cores has proven particulary useful as it provides a historical record of the various influences on the aquatic system by indicating both the natural background levels and the man-induced accumulation of pollutants over an extended period of time. Since adsorption of pollutants onto particles is a primary factor in determining the transport, deposition, reactivity, and potential toxicity of these materials, analytical methods should be related to the chemistry of the particle's surface and/or to the pollutant species highly enriched on the surface.
New objectives regarding the improvement of water quality as well as problems with the resuspension and land deposition of dredged materials require a standardized assessment of sediment quality. Biological criteria integrate sediment characteristics and pollutant loads, while generally not indicating the cause of effects. With respect to chemical-numerical criteria immediate indications on biological effects are lacking; major advantages lie in their easy application and amendment to modeling approaches. Numerical approaches, on the one hand, are based on (1) accumulation; (2) pore water concentrations; (3) solid/liquid equilibrium partition (sediment/water and organism/water); and (4) elution properties of contaminants. The second component in an assessment scheme would include characteristics of the solid substrate, in particular, buffer capacity againt pH-depression. At the present stage of criteria development we propose that the substrate properties should be classified on the basis of the carbonate and sulfide inventory, whereas the pollutant load is advantageously assessed by the accumulation rate multiplied with a toxicity factor for the respective substance.